Rare earth complexes have been continuously utilized as fluorescence and phosphorescence-emitting materials in the fields of electroluminescence and white LED illumination; the field of luminescent ink; the field of luminescent plastics; and the like. In each of these fields, rare earth complexes are expected to be compatible with organic solvents and resins.
Examples of rare earth complexes having compatibility with organic solvents and resins are given, for example, in Patent References 1 and 2 and in Nonpatent Reference 1. The complex described in Patent Reference 1 is linear tetraphosphine tetraoxide. The complex described in Patent Reference 2 is a complex that is formed as a crosslinked structure of multiple phosphine oxide multidentate ligands and a rare earth ion.    Patent Reference 1: Japanese Unexamined Patent Publication (KOKAI) No. 2010-95514    Patent Reference 2: WO2012/150712    Nonpatent Reference 1: K. Miyama, Y. Hasegawa et al., ChemPlusChem, 2012, 77, 277-280Patent References 1 and 2 and Nonpatent Reference 1 are hereby incorporated in their entirety by reference.